1. Field of the Invention
The present invention relates generally to the field of nuclear power generation and in particular to a new and useful lattice bar support for retaining and positioning water tubes within a nuclear steam generator.
2. Description of the Related Art
One known type of lattice support is manufactured by Babcock and Wilcox Canada Ltd. The lattice support has an array of bars arranged in a diamond grid pattern for supporting the multiplicity of water tubes in the steam generator. The bar array is supported by a peripheral heavy structural ring, which is connected to the outer shroud and shell of the steam generator. The bars transmit the support load to the ring, which conveys it in turn to the shroud and shell.
The bars in the array are arranged parallel to one of two directions and when bars of different direction cross over each other, they form angles at bar intersections of 60xc2x0 and 120xc2x0.
The bars are of two types, high bars and low bars. Low bars comprise the majority of the bars in the array and are about 1 inch high. High bars about 3 inches in height are used about every 4 to 8 bars in the array and have slots in their edges to permit bars arranged in the other direction to cross at the same level within the peripheral ring. The slots are typically 1 inch deep for low bar intersections and 1 xc2xd inches deep for high bar intersections. The high bars are used to help position the low bars within the array and to transmit accumulated load to the peripheral ring.
The known high bars have flat sides which contact tubes positioned in each of the channels formed by two pairs of differently oriented bars. The contact area with the tubes is greater with high bars than low bars. The contact area is subject to greater risk of corrosion and rupture due to interactions between materials in nuclear steam generators. The larger the contact area, the greater the risk of corrosion and/or cracking of the water tubes, which will in turn lead to release of contaminated pressurized water from the tubes. Further, due to the greater contact area between tubes and high bars, eddy current inspection techniques for detecting cracks and tube damage are less reliable in these regions.
It is an object of the present invention to provide a lattice bar support which reduces corrosion and/or cracking of tubes in nuclear steam generators.
It is a further object of the invention to provide a lattice bar support which reduces the probable size of tube ruptures from corrosion due to contact with the support.
Accordingly, a lattice high bar is provided having scalloped indentations along its length. The scalloped indentations are located at points on the high bar where water tubes will contact the high bar. The indentations extend from one edge of the high bar to a point about two thirds of the way across the bar. When the high bars are used in a lattice bar array, only the unscalloped portion of the high bar contacts the adjacent supported tube, thereby reducing the contact area and the likelihood of corrosion and cracking.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.